J. T. Jut son — Rounding of Pebbles. 433 



ern Australian goldfields, have in places become quite 

 rounded on those portions exposed to the weather since 

 their removal from below the surface; and the beating 

 of rain appears to be the cause of this. 



At a mine inspected by the writer, a number of green- 

 stone pebbles, well-rounded and apparently truly water- 

 worn by abrasion, were shown as having been ordinary 

 angular fragments brought to the surface and rounded 

 by water splashing them from the pump. This explana- 

 tion was not accepted as genuine at the time, although 

 the good faith of the informant was not questioned ; but 

 the pebbles were regarded as having by some mischance 

 found their way to their then position. In view, how- 

 ever, of the observations on which this paper is based the 

 writer believes that the statement made as to their origin 

 is probably true. 



The greenstones of the "Western Australian goldfields 

 are usually much altered rocks chemically and miner al- 

 ogically, and this alteration may assist the mode of 

 weathering here described, but further investigation is 

 necessary to come to a conclusion on this point. 



Comparison with rock fragments in adjacent Canyons. 



The country of which the greenstone hills referred to 

 above form a part, is dissected into young steep V- 

 shaped canyons up to 100 feet in depth, which are 

 entirely due to normal stream erosion. Consequently, 

 it is interesting to compare the greenstone rock frag- 

 ments there found with those described in this paper. 

 Careful observation shows that the rock debris of the 

 stream channels is, on the whole, angular or sub-angular, 

 hardly any fragments having more than their corners 

 rubbed off and blunted. The rounded forms described 

 in this paper are quite absent, so that it is clear that 

 stream abrasion under present conditions cannot pro- 

 duce these forms. As, however, the stream channels are 

 dry nearly all the year it is difficult to understand— if 

 past erosive action be rejected — why such rounded peb- 

 bles are not produced in the stream beds by the same 

 agents that are producing them on and at the foot of the 

 hills as described in this paper, especially as the stream 

 rock fragments are of similar rocks and largely free 

 from iron films. The only suggestions as to the reason 

 of this that the writer can make are that the rock frag- 



